Dynamic Measurement of Volatile Organic Compounds (VOCs) for Real-time Characterization of Soil Microbial Metabolic Response to Simulated Snowmelt

Microorganisms regulate the transformation and flux of photosynthetically derived carbon in soils and are central contributors to global biogeochemical cycles that sustain primary productivity. Observing microbial metabolism and its dynamics and response to perturbation non-destructively remains a major challenge for systems such as soil. Many `omics approaches exist to interrogate biomolecular processes performed by the soil microbiome, although all require sample retrieval and processing, while non-destructive approaches such as the monitoring of trace gases could be considered `information-rich' although not `information-dense' and therefore provided more limited insight into mechanistic processes underlying their fluxes. Microbial volatile organic compounds (mVOCs) emitted from soils represent moderately information-dense signatures and when assayed using state-of-the-art instrumentation such as Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-TOF-MS) provide information-rich insights into the metabolism of active microbiomes, over time and non-destructively. In this study, we used PTR-TOF-MS to non-destructively investigate the metabolic trajectory of microbiomes from montane meadow soils, and their response to a simulated wet-up event akin to the snowmelt period of the water year. Using an information theory approach based on mutual information we identified metabolite pairs with robust interactions, including those that were non-linear and with time lags. Biological relevance of observed mVOC interactions was evaluated by projecting the connections onto the KEGG reaction network to allow for interpretation in the context of known metabolic pathways. Putative connections were constructed into a network where acetone, isoprene and acetate emerged as metabolic hubs indicative of the interactions between microbial litter decomposition, methylotrophy and fermentation as well as other metabolic processes important for global biogeochemical cycles.